Submarine signaling apparatus



April 27 19%.

w. L. WALKER SUBMARINE SIGNALING APPARATUS Filed may 11. 1921 4Sheets-Sheet 1 LLJJ Iwveutor 'wzuiam-L.mmer

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April 27,1926.

' W. L. WALKER SUBMARINE SIGNALING APPARATUS Filed m 11. 1921 4Sheets-She 2 as? 30 zz jiivefifii' HALE naval.

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w. 1.. WALKER SUBMARINE SIGNALING APPARATUS Filed May 1 1921 4Sheets-Sheet :5

April '27 1926.

I w. L. WALKER SUBMARINE SIGNALING APPARATUS Filed May 12., 1921 4Sheets-Sheet 4 CiamL. Maker wtl'orfieya Patented Apr. 27, 1926.

UNITED .STATES PATENTT OFFICE.

WILLIAM L. WALKER, OI NE'W.YOBK, N. Y., ASSIGNOB TO WALKER SIGNAL ANDEQUIPMENT CORPORATION, OF NEW YORK, N. Y., ACOBPORATION OF DELAWARE.

SUBMARINE SIGNALING APPARATUS.

Application filed Kay 11, 1921. Serial No. 468,611.

Signaling Apparatus, of which the follow mg is a. specification.

This invention relates to signaling systems and more particularly to asound re ceiving device or ear for use in such systems. is employed onship board for receiv ng sound vibrations propagated through the waterit is necessary to locate it at a point well below the water line; Thecommon practice heretofore has been to attach a tank containing water,in which microphones. are immersed, to the. inner skin of a ship; Thesound coming through the water, passes through the skin of the ship,enters the water in the tank and is picked up by the microphones. Suchan arrangement is objectionable because the waves-and the passage of theship through the water produce water noises. Further as the tankscontain water, the inner noises of the ship, such as sounds from theengines, are readily transmitted to the microphones, with the resultthat weak signals which it is desirable to hear, are blanketed ordrowned out.

V The principal object of the present invention is to overcome thedefects incident to the use of-sound receiving devices such aspreviously have been used in connection with the receipt of submarinesounds, and espeeially to improve thoseemployed' on shipboard. To thisend it is proposed to so construct the sound receiving box or ear asthat one of its sides shall be its receiving diaphragm, the outersurfacd of which will be substantially flush with the outer skin surfaceof the plating of a ships hull. To secure the greatest sensitiveness toweak sound impulses, this diaphragm is made thin and its distortion, dueto hydrostatic pres sure on its outer surface may be compensated for byair pressure as set forth inmy previous application Serial No. 176,299filed June 22, 1917. In devices of this general character, however, itis not absolutely necessary to provide pressure upon the inner surface othe diaphragm substantially equal to' that ofthe external water pressureWhen a sound receiving device' upon the outer face thereof to insure itsoperation, although this method-is preferred.

As a. diaphragm .02 of an inch in thickness constructed ln accordancewith. the present invention will withstand a pressure of sixty poundsper square inch without collapsing,

so diaphragms of a thickness sufficient to withstand the, external Waterpressure may readily be provided in cases where compensitlion byhydrostatic pressure is not desira e.

A further object of-the invention is to provide a water tight box ofsuflicient strength to withstand the external water pressure so that incase the diaphragm is ruptured the sea water 'will be held in the boxand not be permitted to enter the vessel. Another object of thisinvention is to surround the microphones with air and as air is a. muchpoorer conductor of sound than.

water the microphones are insulated from the ships internal noises to aconsiderable extent.

In accordance with the arrangement herein disclosed the listening devicecomprises an air tight housing secured against the ships side upon theinside of the hull and enclosing a vibratory arm supporting the currentvarying microphones with a minimum of frictional resistance and Withoutlost motion, and without supporting the current varying device upon thesound responsive device. This method ofsupporting the currentwaryingdevice permits the utilization of a plurality of such devices in cooperative or in amplifying relationship with a .single sound responsivedevice and is referred to in my previous application Serial No. 202,680,filed. Nov. 19, 1917. As such housings are usually of steel or iron,from considerations of durability and low cost, it is evident thatsounds transmitted along the hull plating or noises within the ship mayseriously interfere with the receipt of desired sounds or signals so afurther object of the outer surface of the diaphragm. In

fitting the device to an opening in a ships plating, more or less of thethickness of this flange may be cut away, whereby to bring the outersurface of the diaphragm flush with the outer surface of the hull. Thusthe device may be made of a stock pattern and interchangeably fitted toany ship, as desired. As the diaphragm is in fixed relationship with thebody of the housing and with the outwardlyprojecting flange, alldiaphragms will be interchangeable with all ships irrespective of thevariousthicknesses 0f ships plating.

In devices of the class to which this invention relates it has beenusual to employ a microphone supported by the sound responsive devicefor transferring the vibrational motion of the latterint'o electricaloscillations of an observable character. In employing microphone meansfor this purpose, owever, it is desirable to employa pair or more ofsuch instruments arranged in cooperative, amplifying, or in otherrelationship which is readily accomplished by supporting them on avibratory arm or lever attached to a single sound responsive device. Inthe use of such a lever great difiicnlty has been experienced,particularly on ship-board in providing a suitable fulcrum or hearingtherefor-which while providing the necessary delicacy of poise as topractically eliminate friction and lost motion is able to securelyretain the lever in position regardless of heavy shocks or displacementscaused by wave action. The elimination of 10st motion is particularlyimportant inasmuch as the amplitude of vibration of the parts may beless than one-tenth of a millimeter, and if the lever is free to move onits strand or-filamentof suitable material fixed bearing to theslightest degree there may be sufficient lost motion to affect themicrophones. Further any play in-the hearing will allow the lever torise and fall or to rattle, producing corresponding noise inthemicrophones which may blanket a Weak signal. A further object of thepresent inven-' tion is to overcome the difficulties previouslyexperienced in the use of such a microphone lever, as above pointed out.To this end the lever may be supported by securing a taut at its endsand preferably having those portions lying between the lever and itsends under normally equaltorsional strain but in an opposite sense.- Thelever as thus arranged may be considered asv a torsional balancenormally in substantially neutral equilibrium andwhile delicatelysensitive to vibrations of the diaphragm, the lever as thus mounted issecured against bodily displace: ment in a very substantial andefiective manner. For practical considerations the filament employedmaybe double, the two elements thereof passing upon opposite sides ofthe lever and the twist imparted thereto will in such case cause the twostrand elements to be twisted together. To reduce the weight of thelever and therefore its inertia the le. ver is made of U section and isperforated at intervals inits length. In these perforations smallweights may be inserted to change its balance or its period ofvibration.

The microphones are. connected in series or parallel so that theirellects may be averaged and matched with similarly connected microphonesin ears on the opposite side of the ship. Furthermore, with thisarrangement,- if one microphone fails to function properly, the systemwill not become unoperative.

As a preferred embodiment of means for carryingthe above objects intoeli'ect that illustrated in the accompanying drawings. may be employedand wherein Fig. 1 is a vertical cross section showing the device asapplied to the side of a ship, the section beingtaken substantially onthe line a-b of Fig. 3 and showing a portion of the ships plating; Fig.2 is a substantially horizontal cross section of the device of Fig. 1taken on ,aline such as cd of Fig. 3;

Fig. 3 is a vertical cross section substantially at right angles to thesection of 1;

Fig. 4 is a fragmentary cross section on the line -7 of Fig. 3;

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Fig. 5 is a fragmentary vertical cross see section of the devices shownin Fig. 5';

Fig. 7 is a cross section on a line such as 'm''n of Fig.6;

Fig. 8 is a plan view of certain of the dev1ces shown inFigs. 5 and 6,portions thereof being in section; and v Fig, 9 is a diagrammaticelevation illustrating the arrangement of several listening devices in asingle housing.

Referring to the drawings, a portion of the ships outer plating or skinis indicated at 1, such plating having an opening of suitable size forthe reception of the diaphragm housing 2. This housing is preferably ofgenerally cylindrical form and is provided with a radial attachingflange 3. This flange has a series of openings or slots 4 therein forthe reception of attaching bolts 5, by means of which the housing issecured to the ships plating at a point below'the water line and uponthe inside of the ships hull. The outer face 6 of the housing presents asubstantially plain surface and is intended to lie flush with the outersurface of 1 the ship's hull. In the commercial manufacture of devicesof the class herein disclosed the flange 3 will be made of standardthickness with the surface 7 thereof at a predetermined distanre fromthe plane of the surface (SI This distance is such that when the housingis insertei'l within an opening in the hull of a vessel having light orthin plating, the surface (5 will be positioned in the plane of theouter surface of such plating, space being left, however, for theinterposition of a suitable washer or gasket 8 for forming a tightjoint. When the device is to be applied to a ship having thicker platingit is merely necessary to cut away some of the material of the flange 3from the surface 7, thus increasing the distance between such surfaceand the surface 6. The latter surface may thus be located in the planeof the outersurface of the plating regardless of the thickness of'thelatter. In applying the device to an opening in a ships plating, suchopening will preferably be of a diameter somewhat greater than thecylindrical portion of the housing and a bushing 1 of lead or othersuitable material will be inter posed between the ships plating and-thehousing.

Inwardly of the flange 3 the housing is provided with a second flange 9and to this flange may be secured a cover plate 10 by means of boltssuch as 11. In order to prevent leakage beneath the cover plate 10 agasket12 of lead or other suitable material may be interposed betweenthe same and the fiange.9.' The housing is provided with a chamber 13,and in order to prevent or obstruct the passage of sounds from theinterior of the ship into such chamber, a block of insulating material14 may be laced im- "mediately within the plate 10.

uch, plate may be of lead or any other material having sound deadeningqualities. If desired, more or less of the surface of the side walls ofthe chamber 13 may also be insulated against the passage of sounds as bymeans of the insertion of a lead lining 15 therein or ,in any otherdesired manner. At one side of the housing 2 there extends from thecylindrical portion a hollow boss 16 providing an extension 17 of thechamber 13 for a purpose to be hereinafter described. Threaded openings18, 19 may be formed in. the wallsof the housing for the attachment ofafpressure regulating device, it'suchbe employed, and for the insertionof a plug or other, suitable device through which pass the electricconductors leading to the interim of the housing.

Atits outer portion the cavity within the housing gs provided with anannular seat 20 w "ch engages a flange 22 formed updiap unit or cell 21.This dia-v hragmunit is'preferably providedwith an inwardlyextending'flange 23 for engage 36, 37 are a pair of filaments 48, 49.

ment by a suitable tool for removing the unit from its seat whendesired. For retaining the diaphragm unit or cell in position againstits seat a collar 26 may be provided, such collar being externallyscrcw-threadcd for engaging screw threads 27 upon the interior ot thehousing. interposed between the collar 26 and the diaphragm unit 21 maybe a gasket 29 of rubber or other suitable material. To permit the readyturning of the collar 26 in screwing the same into place, it is providedwith angularly disposed faces 28, so arranged as readily to be engagedby a wrench of suitable form. The diaphragm units, constructed asdescribed, are interchangeable and while particularly intended for usein the manner and for the purpose described may be found useful in othersituations.

The diaphragm unit or cell 21 is in the form of a ring of substantialthickness and some suitable material such as steel, and the diaphragm 24which extends across and closessuch ring is preferably formed integrallytherewith. This diaphragm may be made of properthickness to withstandany hydrostatic pressure to whichit may be subjected in normal usewithout the necessity of counterbalancing such pressure upon the innerside thereof, although pressure preferably will be maintained within thehousing sufficient to'relieve the diaphragm from the efle'cts ofunbalancedpressure upon its opposite faces. At its center the diaphragmis provided with a boss 25 for a purpose to be hereinafter described,

, Secured upon the interior of the housing and'within the chamber 13 isa bracket 30,

such bracket being attached to the housing as by means of screws 31.Outstanding from the bracket 30 are a pair of spaced supporting members32, 33, such members being provided with aligned openings 34, 35,respec-' tively.. W'ithin the gpenings 34, 35 are arranged a pair ofsubstantially cylindrical plugs 36, 37, respectively, such plugs eachhaving a longitudinal slot, as 38, 39. Engaging the slots 38, 39 arepins 40, 41 fixed. within the supports 32, 33, respectively, and servingto preventrotation of the plugs -within the openings in such supports,but

permitting longitudinal adjustment, of the same. The plugs 36, 37 areexternally screwthreaded at their outer portions, as indicated at 42,43, and are provided with axial bores 44, '45 extending therethrough.Ad-- justing nuts 46, .47 engage the screw threads 42, 43, respectively,such nuts also engagingthe outer surfaces of the supports 32, 33. Bymeans of the nuts the plugs may be adjusted within the openings inthesupports. Lock nuts may also be provided if desired for retaining. theplugs in adjusted position. Passingthrough the bores in the pangs esefilaments may be, and preferably are, of steel, such for example aspiano wire, although it is contemplated that other matcrials might beemployed as circumstances might warrant. \Vhile these filaments may beentirely independent one to the other, as shown herein, they are soconnected as to form a substantially continuous band, such band beingdoubled together whereby to form the looped portions 50, 5t. Passingthrough the looped portions of the band are pinsoz, 52 respectively,such pins extending across the bores in the plugs and thus serving in aconvenient manner to prevent the withdrawal of the filaments from thebores in the plugs. In the preferred arrangement the boresin the plugsmay be enlarged at their inner ends as indicated at 54, 55, in order toavoid contact of the filaments with the side walls of the bore.

56 is a lever device herein shown as comprising the web member 56 and apair of parallel flange members 56", 56 (Fig 8) respectively, the leverbeing thus of substantially channel section. At a point near the centerof length of the lever. the flanges 56, 56 are provided with alignedopenings substantially in the plane of the adjacent sur face of the webmember 56" and through such openings passes one of the filaments as 49.The other filament 48 lies in engagement with the other surface of theweb member 56 and for securing such filaments to the lever memberclamping. plates 57, 58 are employed, such plates being secured to thelever by means of screws or bolts 59. With this arrangement it isevident that the filaments pass on opposite sides of the web member ofthe lever and transversely of the axis thereof, the central portions ofthe filaments being securely clamped to the lever. Thefilamentsconstitute the fulcrum or pivot for the lever, .and by suitablyadjusting the nuts-46, 47 the filaments may be put under heavy tension-whereby the lever member is properly suported and, prevented fromaccidental bodily displacement. In the preferred arrangement,as-indicated in F ig. 6, the end portions of the filaments, that isthoseportions lying at either side of the lever 56, are twisted togetherbut in opposite directions, and thuswhen placed under tension theindividual strands constituting the doubled filament are placed under aconsiderable torsional'st-rain. As the strain is in opposite directions,however, at theopposite sides of the lever, and as the amount of twistis substanially equal, all tendency to turn the lever in one or theother direction is eliminated and thus tbe lever may be considerednormally to occupy a position of neutral equilibrium.

Within the chamber 13 are arranged a. pair of microphones 60, 61 one ofsuch micro phones being placed in the cylindrical portion of the chamberand the other in the extension 17 thereof. These micro hones areoppositely disposed and are locate upon opposite sides of lever 56 andsubstantially at the ends thereof. The vibrator elements of themicrophones are adjustably connected to the lever 56 as by means of thescrews 02 en gaging with the internally threaded sleeves (33 mounted insuitable openings in the respective ends of the lever 56. That end ofthe lever 56 adjacent the microphone ,60 is provided with an opening forthe reception of a rod 64, such rod being attached at its opposite endto the boss 25 of the diaphragm 24. Nuts 65, (36 are provided wherebythe connection of the rod (34 to the lever 56 may be suitably adjusted.

In order to decrease the weight of the lever 56 the latter is providedwith a series of openings 67 spaced apart longitudinally thereof. Theseopenings also serve as sockets'for the reception of weights such as 68,these weights serving to permit the initial balancing of the lever andalso if desired by the addition of more or less weights upon oppositesides of the fulcrum serving. to change the period of oscillation of thelever about such fulcrum. Secured to the outer ends of the supports 32,33 is a plate 69, such plate serving as a convenient support for theterminals of electrical connections, which may be introduced into thecasing through one of the openings 18 or 19.

In the arrangement for a plurality of instruments shown in Fig. 9 asviewed from the inside with cover removed and before assembling partsthe housing. 70 is indicated as of elongated rectangular form, andprovided with a series of openings for the reception of the diaphragmholders such as 71, 72, and 73, such holders being seated withinindependent chambers in the housing. With this arrangement severallistening devices or cars may be applied simultaneously to the shipshull at a relatively short distance apart, and this may befounddesirable under certain circumstances. It is contemplated, however,that under ordinary circumstances the listening devices or carscomprising housings 2 with the associated parts and such as hereinbeforedescribed will be located at separated points on the ship and that. theelectrical conducting wires leading therefrom will converge to a commonstation.

In the operation of the device, it being understood that the housing hasbeen ape plied to a suitable opening in the ships hull below the waterline and that the diaphragm 24 lies in the plane of the outer surface ofthe ships hull, any sound vibmtiontrans mitted through the water andimpingingupon the diaphragm, will immediately. set the latter in -motionand through the lever 56 will actuate the inicrophones'60, 61. By

the employment of a rigid lever for connecting the microphones there issubstantially no loss of vibrational intensity therebetween, and bymounting the vibration-transmitting lever in the manner hereinabovedescribed, it is evident that it is extremely sensitive to allvibrations imparted by the diaphragm, while at the same time it issubstantially impossible for heavy shock or rolling of the ship to causebodily displacement of the lever from its bearing, the filamentoussupport therefor retaining the same in normal position under allconditions. By making the diaphragm integral with its cell or unit it ispossible to secure the desired resiliency of the same, while at the sametime providing the necessary strength.

, It may be found under certain circumstances that the amplitude of thevibrations received by the diaphragm is so small that no appreciableoscillation of the lever 56 about its fulcrum will be imparted thereto,but with the arrangement described it is found that even under suchcircumstances the vibrations are impressed upon and are transmittedalong the lever to the microphones. Thus whether or not the leveractually oscillates about its pivot the desired results are obtained.

Having thus described the invention in a preferred embodiment of thesame, what I claim and desire to secure by Letters Patent of the UnitedStates is 1. A submarine ear comprising a casing having a seat thereinand a threaded portion adjacent the seat, a diaphragm cell engaging saidseatfa threaded collar engaging the threaded portion of the casing forretaining said cell in engagement with said seat, a re silient washerinterposed between said cell and collar, a microphone within the casingspaced from and supported independently of the diaphragm, and means fortransmitting vibrations from the diaphragm to the microphone.

2. A sound receiving device comprising a water-tight housing having adiaphragm constituting a portion of its wall, a micro--, phone withinthe housing spaced from the diaphragm and supported independently of thelatter, and means for transmitting vibrations of the diaphragm to themicrophone com, rising an elongate rigid rod perpendicu ar to the planeof the diaphragm.

3. A sound receiving device comprising a water-tight housing having adiaphragm constituting a portion of one of its walls, a plurality ofmicrophones disposed within the housing and supported independently ofthe diaphragm, and means for transmitting vibrations from the diaphragmto the microphones comprising an elongate member of small transversesection said member be ing-perpendicular to the plane of the diaphragm.

4. A sound receiving device comprising a heavy thick walled casing, a.diaphragm forming a portion of one wall of the casing, a microphonesupported within the casing independently of the diaphragm, means ineluding a pivoted lever for transmitting movement from the diaphragm tothe micro phone, and sound deadening means for guarding the microphonefrom vibrations other than those transmitted from the diaphragm.

5. A. submarine ear comprising a housing having a chamber therein, asound receiving diaphragm for closing one side of said chamber, thewalls of the housing being thick as compared with the diaphragm, soundactuated instrun'ientalities within said chamber,

and a thick block of sound deadening ma terial within said chamber andextending substantially across that side of the chamber opposite thediaphragm.

6. A device of the class described comprising a thick walled housingprovided with a chamber, a thin diaphragm for closing one end of saidchamber, a thick block of sound deadening material within said chamberand spaced from said diaphragm, sound actuated instrumentalitiesinterposed between said diaphragm and block, and sound deadening meanslining other portions of the' walls of the chamber.

7. A sound receiving device comprising a water tight housing, adiaphragm forming one wall of the housing, a plurality, of microphonesin spaced relation within the housing, a rigid member extending betweensaid microphones for transmitting vibrations thereto, and means forconnecting said member with the diaphragm.

8. A. device of the class described comprising a water tight housing, adiaphragm forming one Wall of the housing, a pair of oppositely disposedmicrophones spaced within the housing laterally one from the other, arigid bar extending from one of the microphones to the other and havingthem disposed respectively upon its opposite sides, and means forconnecting said bar to said diaphragm.

9. A sound receiving device comprising a. water tight housing having achamber, a diaphragm extending across the same, a microphone devicewithin said chamber, and

1 a rigid member for transmitting vibrations a pair of microphones saced laterally one from the other, a pivoted lever member fortransmitting vibrations to the said microphones, and means whereby theperiod of oscilation of such lever may be varied.

12. In a submarine ear, in combination, a centrally pivoted rigid levermember, microphones disposed respectively upon opposite sides of saidlever adjacent to its ends and in vibration receiving relationshipthereto, and means whereby said lever may be bal unced about its pivotpoint.

13. A microphone connecting lever for use in a sound receiving devicecomprising an elongated substantially rigid member having a plurality ofsocket openings spaced longitudinally thereof, and a weight forselective engagement with said openings.

14. A device of the class described, comprising a lever member, afilament arranged at substantially right angles adjacent its center, aclamp device for securing said filament tosaid lever member, andadjustable means for tensioning said filament.

15. In a device of the class described, in combination, a microphoneconnecting lever, and means providing a fulcrum therefor, said meanscomprising a filament fixedly secured to said lever and extendingtransversely thereof, and means engaging the 0pposite ends of saidfilament for holding it in taut condition.

16. In combination in a submarine ear, a vibration transmitting lever,and means providing a fulcrum for said lever comprising a filamentsecured to'said lever adjacent the center thereof and extendingtransversely thereto, the end portions of said filament being normallyunder substantially equal and opposite torsional strain, and

means engaging the opposite extremities of said filament for supportingit in taut condition.

17. A lever device for use in submarine ears, and means providing apivot for said lever comprising a pair of filamentous strands extendingtransversely of said lever and" secured thereto, the end portions ofsaid strands being twisted together but (in opposite directions. Y

18. Imcombination with a microphone connecting lever, fulcrum meanstherefor comprising a pair of filaments. arranged respectivelyupon-opposite sides of said lever and secured thereto, the end portionsof said filaments being twisted together and in opandmeans engaging the.

posite directions, extremities of said filaments for supporting the samein taut condition.

19. In a device of the class-described, a

lever supporting filament, a member having an opening thereinfor'thepassage of the filament, a pin extending transversely across saidopening and engaging a loop of said filament whereby to'prevent thewithdrawal of the filament therefrom, and means for impartinglongitudinal movement of said member.

20. In a device of the class described a lever supporting filament andmeans for imparting tension thereto comprising a cylindrical plug havinga longitudinal bore for the passage of the filament, a fixed pinengaging a longitudinal slot in said plug whereby to prevent rotationthereof, means to restrain said filament against withdrawal from thebore, and means for imparting longitudinal movement to the plug.

21. In a listenin device, spaced supports having a pair of alignedperforations, plugs slidable in said perforations, said plugs hav inglongitudinal bores extending therethrough and having screw threads upontheir exterior surfaces, adjusting nuts engaging said screw threads, adoubled filament passing through the bores in the respective plugs, pinsengaging the opposite ends of said filament whereby to preventwithdrawal of the same from theplugs, a lever member extending betweensaid supports and means for clamping a strand of said doubled filamentupon eitherside of the lever.

22. A sound receiving device, including a casin having a chamber and alateral offset, a iaphragm forming a closure for thechamber,'.microphones in the chamber and the oifset, and operativeconnections between the microphones and diaphragms for actuation of theform by the latter.

23. A sound receiving device, including a casing having a chamber and alateral offset, a diaphragm forming a closure for'the chamber,microphones in the-chamber and the ofi'set, means interconnecting themicrophones for simultaneous operation, and 0perative connectionsbetween said means and the diaphragm for actuating the parts.

24. A sound receiving device, including a casing having a chamber and alateral offset, a diaphragm forming a closure for the chamber,microphones in the chamber and the oifset, means interconnecting themicrophones for'simultaneous operation and operative connections betweensaid means and the diaphragm, said micro-phone connecting meansincluding an intermediately pivoted lever and the operative connectionincluding a rod extending from lever to diaphragm. '25. A sound earincluding spaced sound actuable members and a lever connecting themembers, said lever being of U-shape in cross section and having aplurality of longitudinally spaced weight receiving apertures formedtherein.

26. A sound receivin device foruse on. 'slii p board comprising a ousingconstructed and arran ed to be seated in an openinggasket interposedbetween the housing and the plates of the ship, a dia hragm forming aportion of the outer wa ing, sound deadening material lining a portionat leastof the interior walls of the housing, a micro honedisposedwi-thin the housing spaced pendently of the diaphragm, and meansfor transmitting vibrations of the latter to the microphone.

27. A sound receiving device comprising a'water-tight housing, aremovable and replaceable diaphragm cell having a diahram adapted toform one wall of the ousing, a plurality of microphones in spacedrelation within the housing, a rigid lever member supporting saidmicrophones and adapted to transmit vibration thereto, whereby to set upvariable currents. in the l of the housrom and supported inde--microphones, and means connecting said lever to the diaphragm. 28. Adevice of the class described comprisingv a water-tight housing having achamber, a diaphragm extending across the same, a plurality ofmicrophone devices within the housing, each of said micro-,2 phoneshaving a vibrator element, a lever within the housing,and rigid meansconnecting' the levervto thediaphragm and also to the vibrator elementof each. of the several devices so that the lever transmits vibrationsof the vibrator elements and thereby produces a variable current in eachmicrophone, 7

Signed by me at Boston, Massachusetts, this seventeenth day of December,1920.

WILL AM L. WALKER.

diaphragm to the several

